Foamable molding compositions containing chemical blowing agents are known. U.S. Pat. No. 3,888,801 discloses the chemical blowing agents which are suitable in the context of the present invention. Resins which are suitable in the present invention are also disclosed in that patent. Also known are the anhydrides of the invention; U.S. Pat. No. 4,420,584 discloses glass filled polycarbonate compositions having an improved impact strength, containing these anhydrides. The art however does not appear to have recognized the unexpected advantages associated with the combination of these components in the context of the present invention.